Math

Problem 1: Two ladders are criss-crossed against walls of height 3 and 5. At what height do they intersect? Problem 2: I take 3 hours to complete a job, and you take 5 hours to do the same job. How long does it take if we work together? This video demonstrates that both problems have

Our Pi Playlist (more videos): http://bit.ly/PiPlaylist The State of Indiana nearly passed a law which would have made Pi equal 3.2 – strange but true. More links & stuff in full description below ↓↓↓ More Pi videos from Numberphile: http://bit.ly/W4oDN1 This video features Dr James Grime – https://twitter.com/jamesgrime The video about squaring circles: https://www.youtube.com/watch?v=CMP9a2J4Bqw A

What is the height of the red bar? This puzzle was posted on Math StackExchange by a Math PhD candidate, so I did not feel bad when I was unable to solve it! (Though I suspect some people will even find it “easy.”) Math StackExchange (see solution by Eric Duminil). It was posted by a

Free trial at The Great Courses Plus: http://ow.ly/tKWt306Gg7a Dr James Grime discusses “e” – the famed Euler’s Number. More links & stuff in full description below ↓↓↓ A bit extra from this video: https://youtu.be/uawO3-tjP1c More James Grime videos from Numberphile: http://bit.ly/grimevideos Support us on Patreon: http://www.patreon.com/numberphile NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets:

This simple problem for kids is sure to stump some adults. Can you figure out the height of the table? Problem adapted from #quiz Here is a math word problem from a Chinese elementary school student's homework. Have a try to figure it out! Leave your answer in the comment. pic.twitter.com/kOlydqNDQO — China Focus (@China__Focus)

Professor Tony Padilla on the epic number, TREE(3). Continues at: https://youtu.be/IihcNa9YAPk More links & stuff in full description below ↓↓↓ Graham’s Number: http://bit.ly/G_Number Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science. NUMBERPHILE

Dr James Grime discusses a type of number beyond the complex numbers, and why they are useful. Extra footage: https://youtu.be/ISbJ9S0fzwY More links & stuff in full description below ↓↓↓ Support us on Patreon: http://www.patreon.com/numberphile NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Numberphile is supported by the Mathematical Sciences Research Institute

This little trick makes math calculations much easier. Sources/references (March 2019) Fascinating little life hack, for doing percentages: x% of y = y% of x So, for example, if you needed to work out 4% of 75 in your head, just flip it and and do 75% of 4, which is easier. — stephensben at

Can you solve this interesting geometry problem? References Solution by “WAY TO GOVT JOB” on YouTube Stretched length of band https://www.thestudentroom.co.uk/showthread.php?t=1936482 Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address at end of many videos). I may not reply but I do consider all ideas! If you buy from the links below I may receive a

Simon Singh on Fermat’s Last Theorem. Simpsons book: http://amzn.to/1fKe4Yo Fermat book: http://amzn.to/1jWqMTa More links & stuff in full description below ↓↓↓ EXTRA FOOTAGE: http://youtu.be/FXbsIbRVios FERMAT IN SIMPSONS:http://youtu.be/ReOQ300AcSU Interview with Ken Ribet, who played a big role: https://youtu.be/nUN4NDVIfVI Wiles’ proof: http://bit.ly/FermatProof NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Videos by Brady

Ron Graham explains the number which takes his name… See our other Graham’s Number videos: http://bit.ly/G_Number More Ron Graham Videos: http://bit.ly/Ron_Graham More links & stuff in full description below ↓↓↓ Graham’s Number (Numberphile T-Shirt): http://bit.ly/Grahams_T-Shirt See him discuss how big it is: http://youtu.be/GuigptwlVHo Extra footage here: http://youtu.be/rGWuimr5CGQ And our original Graham’s Number video: http://youtu.be/XTeJ64KD5cg Support

The quadratic formula is really useful, but its derivation is confusing to many. Like what is the point of “completing the square” anyway? In this video, I show how “completing the square” has a geometric interpretation–you are actually making the areas of two squares equal to each other! Blog post (text/image summary): http://wp.me/p6aMk-4kG You can

Here’s how you do cube roots in your head! Avoid looking like Education Secretary Nicky Morgan who was stumped when asked to do a cube root: https://www.youtube.com/watch?v=x8CV0dfQMdU Note: the starting number needs to be a perfect cube. So it’s more of a magic trick: ask someone to cube a number and then you can deduce

Why squaring the circle – the old-fashioned way – was found to be impossible? Numblr: http://numberphile.tumblr.com/ More links & stuff in full description below ↓↓↓ This video featuring Dr James Grime: https://twitter.com/jamesgrime The paper from this video on ebay – http://bit.ly/brownpapers NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Videos by

The Nazi’s Enigma Machine – and the mathematics behind it – was a crucial part of World War II. Flaw video at: http://www.youtube.com/watch?v=V4V2bpZlqx8 More links & stuff in full description below ↓↓↓ Brown papers on ebay: bit.ly/brownpapers Dr James Grime demonstrates the machine and discusses its many configurations. James’ “day job” is touring with the

University entrance exams and job interviews have asked questions similar to this problem. What is the area of the rectangle? What is the minimum area of the large triangle? Special thanks this month to: Jamal Jackson, Mike Robertson, Michael Anvari, Robert Zarnke, Fiona Harper, Kyle. Thanks to all supporters on Patreon! http://www.patreon.com/mindyourdecisions Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send

This problem went viral because even teachers had trouble solving it. It even got covered in television news! Can you figure it out? References BlackPenRedPen Twitter https://twitter.com/blackpenredpen/status/1284719356799115264 BlackPenRedPen video (English) BlackPenRedPen video (Chinese) China Times News Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Like

Check our sponsor The Great Courses Plus (free trial): http://ow.ly/j5cB30hIvm2 This video features Cliff Stoll. More links & stuff in full description below ↓↓↓ More Cliff Stoll videos: http://bit.ly/Cliff_Videos Buy a Klein Bottle from Cliff – it’s an experience: http://www.kleinbottle.com Discuss this video on Brady’s subreddit: https://redd.it/96x6c4 Numberphile is supported by the Mathematical Sciences Research

The knight’s tour and magic knight’s tour. More links & stuff in full description below ↓↓↓ The first magic tour has an error (my fault in animation) with 62 and 64 transposed…. See here: http://periodicvideos.blogspot.co.uk/2014/01/oops.html Brown papers: http://bit.ly/brownpapers Some good knight’s tour links: Great overview by Ben Hill and Kevin Tostado: http://bit.ly/1hYHoLE Notes and huge

Many students in the UK had difficulty with a similar problem on the GCSE exam. What’s the rectangle’s area, given the three circles are identical with radius r? Watch the video to learn how to solve this problem. Sources Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Playlist to watch all videos on MindYourDecisions: https://www.youtube.com/playlist?list=UUHnj59g7jezwTy5GeL8EA_g Send me your favorite puzzles/suggestions by

The ancient Babylonians used a number system with base 60 (sexagesimal). More links & stuff in full description below ↓↓↓ Tablet image courtesy of Bill Casselman and Yale Babylonian Collection – more at http://www.math.ubc.ca/~cass/Euclid/ybc/ybc.html This video features Thomas Woolley – he tweets at https://twitter.com/#!/thomasewoolley NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe:

The abc Conjecture may have been proven by a Japanese mathematician – but what is it? More links & stuff in full description below ↓↓↓ Feeling brave and want to read the papers by Shinichi Mochizuki – http://www.kurims.kyoto-u.ac.jp/~motizuki/papers-english.html (scroll to the bottom) This video features Dr James Grime who tweets at https://twitter.com/jamesgrime NUMBERPHILE Website: http://www.numberphile.com/

Can you solve this incredibly difficult calculus question? I had a lot of fun solving this one! Special thanks this month to: Kyle, Mike Robertson, Michael Anvari. Robert Zarnke, Fiona Harper. Thanks to all supporters on Patreon! http://www.patreon.com/mindyourdecisions Adapted from Comment by from discussion inHomeworkHelp Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address at end

The famed Poincaré Conjecture – the only Millennium Problem cracked thus far. More links & stuff in full description below ↓↓↓ Ricci Flow (used to solve the problem): http://youtu.be/hwOCqA9Xw6A Riemann Hypothesis: http://youtu.be/d6c6uIyieoo Extra interview footage with Jim Isenberg: http://youtu.be/7eJleW0JcKg Grigori Perelman’s paper: http://bit.ly/perelmanpaper Discussed here by Katie Steckles and James Isenberg. Support us on Patreon:

Albert Einstein was challenged with a simple riddle in a 1934 correspondence with the psychologist Max Wertheimer. Can you figure it out? Thanks to all patrons! Special thanks to: Shrihari Puranik, Richard Ohnemus, Michael Anvari, Kyle. We are the only channel to feature math topics suggested by people around the world. Support on Patreon to

Tadashi Tokieda puts $20 on the line… More links & stuff in full description below ↓↓↓ More Tadashi videos: http://bit.ly/tadashi_vids Paperclips: https://youtu.be/wGkvyN6s9cY Video by Brady Haran and Pete McPartlan (animations by Pete) Support us on Patreon: http://www.patreon.com/numberphile NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets: https://twitter.com/numberphile Subscribe: http://bit.ly/Numberphile_Sub Numberphile is supported by the Mathematical

Hippocrates of Chios solved this, nearly 100 years before Euclid even wrote The Elements, and before we knew the exact formula for the area of a circle. This is said to be the first precise mathematical of the area between two curved lines. Learn how he solved for the area of a crescent-shaped lune (same

Fields Medallist and math “celebrity” Cédric Villani is famous for wearing ornate spiders on his lapel. More Villani videos: http://bit.ly/Villani_Videos Cédric Villani website: http://cedricvillani.org His book Birth of a Theorem (Amazon): http://bit.ly/BirthOfATheorem Villani talks about his Fields Medal: https://youtu.be/Vp3sgYKULp0 Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by

Featuring Professor Howard Masur from the University of Chicago. Filmed at the Mathematical Sciences Research Institute (MSRI). Part 2 of this interview: https://youtu.be/AGX0cLbHaog Patreon: http://www.patreon.com/numberphile Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of

Squarespace: http://www.squarespace.com/numberphile More links & stuff in full description below ↓↓↓ More linguistics on Numberphile: http://youtu.be/SbZCECvoaTA Billion and Trillion: http://youtu.be/C-52AI_ojyQ Tom Scott on numbers and linguistics – a discussion with spans counties, countries, continents and the far reaches of space. Tom’s own channel is: https://www.youtube.com/user/enyay Art and animation by Pete McPartlan http://www.petemcpartlan.co.uk Support us on

A chat about some of the ways legendary physicist Richard Feynman cracked safes (filing cabinets) at Los Alamos during the Manhattan Project. More links & stuff in full description below ↓↓↓ Discussed by Professor Roger Bowley. My Favourite Scientist on Feynman: http://www.youtube.com/watch?v=qoYWfytx5QA Feynman Diagrams: http://www.youtube.com/watch?v=3bbJeMBHq0g Enigma: http://www.youtube.com/watch?v=G2_Q9FoD-oQ NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile

I had a lot of fun solving this one, and I think you will too! 0:00 Problem 0:49 Hints 4:12 Solution Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address at end of many videos). I may not reply but I do consider all ideas! If you buy from the links below I may receive a

Beautiful Dragon Curves, Fractals and Jurassic Park. Featuring Rob Eastaway. More links & stuff in full description below ↓↓↓ Rob’s website: http://www.robeastaway.com/ Thanks to Matthew Ward and Faraz Barzideh who helped Brady out with some curves! The book Jurassic Park is by the late Michael Crichton. NUMBERPHILE Website: http://www.numberphile.com/ Numberphile on Facebook: http://www.facebook.com/numberphile Numberphile tweets:

Your math teacher and friends will be confused, but you’ll look like a genius when you solve multiplication problems with this unusual math trick. Source: I read about this trick from a math book first published in 1956. (Rapid Math Without A Calculator by Frederick Collins). If you like my videos, you can support me

Johnny Ball on Russian and Egyptian Multiplication. Check out Brilliant (get 20% off their premium service): https://brilliant.org/numberphile (sponsor) More links & stuff in full description below ↓↓↓ More on Johnny Ball, including his books and live shows: https://www.johnnyball.co.uk Russian multiplication is also known as Ethiopian multiplication. Why Use Binary? (on Computerphile) – https://youtu.be/thrx3SBEpL8 Discuss on

This problem is adapted from an Oxford University admissions question. They say if you can solve this in your head, you are a genius 😉 Alex Bellos’s column on The Guardian https://www.theguardian.com/science/2021/jul/12/did-you-solve-it-oxford-university-admissions-questions Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address at end of many videos). I may not reply but I do consider all ideas!

French numbers can pose problems for non-native speaker – especially when you move beyond 70. Also discussing problems with phone numbers and commas! More links & stuff in full description below ↓↓↓ Featuring Dr Paul Smith from the University of Nottingham. The French and marks out of 20: http://www.youtube.com/watch?v=QzrRkhU248A A little extra unlisted bit from

A triangle with sides of 4, 3, and 5 is drawn inside a square as shown. What is the length of the square’s side? It’s a fun little geometry problem! Sources https://www.instagram.com/p/Btw9ZfyBz5w/ http://mathhelpforum.com/geometry/236852-area-square-right-triangle-inside.html Egyptian Proverb http://oaks.nvg.org/egyptian-proverbs.html Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Why

Three chords are drawn in a circle, spaced 30 degrees apart from the same vertex. If the left chord is 10, and the right chord is 12, what is the length of the middle chord? Wow! The channel “Freedom Mathematics” did a general case of the chord progression puzzle. The general problem is quite complicated!

Infographics are not new.. in 1862 Charles Joseph Minard created a much-praised infographic depicting Napoleon’s invasion of Russia in 1812. More links & stuff in full description below ↓↓↓ This video features Dr James Grime – http://singingbanana.com More of James on Numberphile: http://bit.ly/grimevideos Here is the info graphic: http://en.wikipedia.org/wiki/File:Minard.png A book coming soon about the

This is a fun little geometry problem. Source Bilal Sarımeşeli tweet #math #geometry #teachertwitter #questiontime Find the radius of the circle. pic.twitter.com/C1l5P2iAvN — Bilal Sarımeşeli (@bilalsarimeseli) September 26, 2019 Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Like many YouTubers I use popular software to

Featuring Ben Sparks discussing the Mandelbrot Set (and Julia Sets). Catch a more in-depth interview with Ben on our Numberphile Podcast: https://youtu.be/-tGni9ObJWk More links & stuff in full description below ↓↓↓ More videos with Ben: http://bit.ly/Sparks_Playlist Ben Sparks website: https://www.bensparks.co.uk And on Twitter: https://twitter.com/sparksmaths Holly Krieger has done a few Mandelbrot videos on Numberphile… The

Three squares are placed in a row. Connect the bottom left corner of each square to the top right corner of the third square, forming angles with measures a, b, c with the horizontal. What is the sum of a, b, and c? Many people requested this problem, and I thank Roberto O. and Cardist

Sequence guru Neil Sloane on a sequence which puzzled him – until he spotted the mistake! More links & stuff in full description below ↓↓↓ More Neil Sloane videos: http://bit.ly/Sloane_Numberphile The OEIS: https://oeis.org Hanny’s Voorwerp: https://youtu.be/RDr6bSB6Vlg Numberphile is supported by the Mathematical Sciences Research Institute (MSRI): http://bit.ly/MSRINumberphile We are also supported by Science Sandbox, a

The problem is a little bit complex, but the answer is delightfully sur-pi-sing! Subscribe: https://www.youtube.com/user/MindYourDecisions?sub_confirmation=1 Send me suggestions by email (address in video). I consider all ideas though can’t always reply! Why are some comments before the video is published? Get early access and support the channel on Patreon https://www.patreon.com/mindyourdecisions If you buy from the